We have proposed to study the translation of Rous sarcoma virus RNA and messenger RNA taken from control and transformed chick embryo fibroblasts. In parallel with this approach, a study will be made of the protein biosynthetic activity of intact cells. In both cases the proteins will be analyzed by polyacrylamide gel electrophoresis, peptide fingerprinting and immunoprecipitation. However, in the case of intact cells a procedure for high-resolution two-dimension electrophoresis of proteins will be very useful. This technique has resolved at least 1000 proteins in a single analysis and can detect a protein that constitutes only 10 to the minus 4th power % of the total protein applied. Therefore, proteins present at levels of only a few hundred molecules per cell can be detected.